The sympathetic drive emanating from the brain is increased in animal models of hypertension and in patients with primary hypertension. The paraventricular nucleus (PVN) of the hypothalamus is an important site for the control of sympathetic outflow through its projections to sympathetically related sites in the brainstem and spinal cord. During the previous funding period, we showed that augmented glutamatergic input contributes to increased excitability of PVN presympathetic neurons and elevated sympathetic vasomotor tone in the animal model of hypertension. However, little is known about the molecular mechanisms underlying the sustained increase in glutamatergic input to the PVN in hypertension. Our recent study suggests that group I metabotropic glutamate receptors (mGluRs) in the PVN are critically involved in the support of elevated sympathetic outflow in hypertension. In this competing renewal proposal, we will use spontaneously hypertensive rats and renovascular hypertensive rats as animal models of hypertension to test our central hypothesis that group I mGluRs are upregulated at presynaptic and postsynaptic sites, which leads to increased glutamatergic input and excitability of PVN presympathetic neurons in hypertension. Our specific aims are to determine (1) the changes in the expression and distribution of group I mGluRs in the PVN during the development of hypertension; (2) the contribution of presynaptic group I mGluRs to augmented glutamatergic synaptic input to PVN presympathetic neurons in hypertension; (3)the downstream mechanisms mediating increased excitability of PVN presympathetic neurons by activation of postsynaptic group I mGluRs in hypertension; and (4) the changes in calcineurin activity and their contribution to increased group I mGluR and NMDA channel activity in the PVN in hypertension. The important roles of group I mGluRs and calcineurin in increased glutamatergic input in the PVN have not been recognized previously. Our proposed studies are expected to unravel a cascade of molecular events responsible for the sustained increase in sympathetic vasomotor tone in hypertension. This new information should have a major impact on our understanding of the fundamental neurogenic mechanisms underlying the development of primary and secondary hypertension and on the design of new treatments for hypertension.